1. Field of the Invention
This invention relates to a hybrid vehicle and, more particularly, to a hybrid vehicle selectively driven by a motor and/or an internal-combustion engine.
2. Description of the Related Art
Hybrid vehicles which combine a fuel fed conventional engine and a motor using clean electric energy have been proposed. Three types of hybrid vehicles are known: a series type in which an engine is used for generating electricity to charge a battery, a parallel type in which the engine is connected to the drive train of the vehicle, and a combined type (a seri-para type) which combines features of the series and parallel types.
In particular, a hybrid vehicle has been proposed (U.S. Pat. No. 3,566,717), in which the generator is connected to the engine, and a part of the output from the engine is used for generating electricity while the remaining output from the engine is directly output through a drive shaft to drive wheels, utilizing a planetary gear unit to combine that direct engine output with output of a motor. This hybrid vehicle is capable of restricting operation of the engine to a highly efficient range, thereby improving fuel efficiency, because all the energy produced by the engine is not used for generation of electricity. Furthermore, the hybrid vehicle can be driven with the engine operating at constant conditions, so that undesirable exhaust emissions can be decreased.
However, the hybrid vehicle disclosed in the aforementioned patent has the engine, the generator and the driving motor all mutually connected through the planetary gear unit and, consequently, it has the disadvantage of disruption of driving comfort caused by each torque change, produced by the engine, the generator and the motor. Further, control of the engine, the generator and the motor, must provide that operation of each should be prevented from interfering with that of the others.